1. Field of the Invention
The present invention relates to apparatus and method for the X-ray computed tomography.
2. Description of the Related Art
The X-ray computed tomographic apparatus (also referred to as the CT scanner) provides information of the subject in the form of images on the basis of the intensity of X-rays having passed through the subject, and plays an important role in many medical practices including diagnosis of illness, treatment and operation planning, etc. The advent of helical scan has made it possible to achieve wide-range data acquisition in a short time.
The patient throughput has become one of critical issues associated with such achievement. Due to ultrafast scans as well as weight saving of X-ray tubes, widespread use of helical scan, increasing number of detector arrays, and enhancement of detection sensitivity in recent years, the patient throughput is influenced more by a time needed for pre-scan setting of the subject than the scan time. The subject lies on his back on the tabletop of the diagnostic table and fine adjusts the body position according to radiologist's instructions. However, only a limited time is allowed for fine adjustment of the body position. Hence, as is shown in FIG. 1A, scans are often performed while the body axis of the subject is tilted with respect to the center line (Z-axis, the rotational axis of the X-ray tube) of the scan range. This results in an event that, as is shown in FIG. 1B and FIG. 1C, the center of the subject is offset from the center of the image and a degree of offset differs from image to image, which makes observations quite difficult.